[RFI] 2.4 GHz Phones
Thu, 3 Aug 2000 16:58:34 -0500
Ed, Eric, and All,
My contact at Siemens is an EMC engineer who has many years of experience
doing the requisite compliance tests. While I can not say for certain, to
answer your question, Eric, my assumption is that he calculated the field
strength based upon either a dipole or biconical antenna, the two types
usually used in that 27 MHz region. Note that there is no required testing
below 27 MHz, so immunity (or lack there of) in our HF bands below 10m is
conjecture. I note that Ed's 34.7 V/m peak calculation is close to the
original 31V/m peak from my contact.
I fully agree with the (several) comments about conducted RF being the
likely problem. I did not state that well in my initial message, but that
is what I was implying with the comments about the use of extensive common
mode protection. That would, of course, be needed on the telephone line
and the power cord from the (probable) wall wart. If the audio or IF
stages still get hammered, then more drastic measures are needed (or find
another cordless phone system).
Note that the system in question complies with the ANSI standard, as
mentioned by Ed, with extra margin in the FM band (as noted by Siemens).
While I have no way of knowing if that margin was prudent thinking to
reduce potential complaints, or response to actual consumer feedback, the
bottom line is that there are a lot more "general" consumers around than
ham operators. A little extra immunity in the FM band is one thing, but
extra margin in a frequency range without required compliance? Won't
happen, at least not anytime soon. One good thing I have been noticing is
that more consumer devices are now "universally" marketed, meaning they
carry not only FCC ID (again, no immunity help), but CE Mark (which does
help) and some others (such as VCCI), as well. That way, manufacturers and
distributors do not need to worry so much about which boxes go to which
country. In return, we hams gain by having our neighbors buying and using
devices which actually have some immunity, be it intentional or not.
I don't know if any of the above helps Wendell, W5FL, who had the original
posting on the subject, but at least we see where the supplier of one
system stands as far as RFI levels are concerned.
Subject: RE: [RFI] 2.4 GHz Phones
> The 31 V/M field for 2Kw PEP 33 feet away seems a bit
> large to me (high by 20 dB or so - what was the antenna gain
By my calculations, 2kW 10 meters away should result in an RMS field of
V/m, assuming 0 dBi antenna gain. This would be 34.7 V/m peak voltage
At the typical angles between antennas and areas where susceptible
may be found, the gain is usually less than 0 dBi. For vertical antennas,
considering real ground losses, about 0 dBi might work. Some beams and
configurations may give higher gain if the beam is low, next to an
building, etc. In that case, 8-12 dBi might be more realistic.
Remember, that figure was for 10 meters distance, pretty close for 2 kW.
Most of the "RF safety" calculations include duty factor, on/off times,
These factors don't apply to RFI; the equipment usually corresponds to the
> Yes, It really would be nice if the FCC requirements
> also specified immunity to EMI fields of 3 V/M or so
> from 500 KHz on up. The vast majority of the Ham's
> EMI complaints would never happen if they did.
The present ANSI standards of immunity for consumer electronics equipment
calls for a radiated immunity level of 3 V/m. More and more equipment has
been being made to this standard and I think there is some reduction in RFI
to consumer equipment as a result. But 3 V/m translates to 100 W to a
dipole 100 feet from the source, nowhere NEAR enough to really offer good
protection from amateur radio.
Ed Hare, W1RFI
ARRL Laboratory Supervisor
225 Main St
Newington, CT 06111
ARRL Web: http://www.arrl.org
ARRL Technical Information Service: http://www.arrl.org/tis/
> -----Original Message-----
> From: Eric Gustafson [mailto:firstname.lastname@example.org]
> Sent: Thursday, August 03, 2000 2:59 PM
> To: email@example.com; firstname.lastname@example.org
> Subject: Re: [RFI] 2.4 GHz Phones
> Hi Dale,
> The 31 V/M field for 2Kw PEP 33 feet away seems a bit large to me
> (high by 20 dB or so - what was the antenna gain assumption?). I
> guess I'll have to get out the books and do a little figgerin' to
> convince myself. I think the last time I did this exercise for a
> typical legal HF station, I got answers mostly in the 2 to 3 V/M
> range. But that is neither here nor there.
> The European specs require immunity to radiated EMI fields of 3
> V/M at frequencies from 27 MHz up. But what is the radiated
> immunity of this particular phone from say 1.7 to 25 MHz? But
> even this is probably not the real issue.
> The real question is: " What is the phone's immunity to
> _conducted_ emissions in the HF frequency range?
> It is very unlikely that the phone is suffering from a direct
> radiated susceptibility problem at HF frequencies. I bet that
> the trouble is really from _conducted_ susceptibility. There is
> probably quite a bit of common mode HF current flowing on both
> the power and signal wiring to the base station for the phone.
> Fortunately, both of these common mode paths are treatable
> external to the phone. Apparently, Uniden has decided to include
> at least some common mode rejection for this type of EMI inside
> the phone.
> Yes, It really would be nice if the FCC requirements also
> specified immunity to EMI fields of 3 V/M or so from 500 KHz on
> up. The vast majority of the Ham's EMI complaints would never
> happen if they did. And the noise generated by many
> "unintentional radiators" would be greatly reduced as well.
> 73, Eric N7CL
- - - - - - - - - -
> >The usual complaints that I see are that our Gigaset 2420 system
> >interferes with video senders and other 2400 MHz devices. I can
> >tell you this, it has been tested to show compliance with IEC/EN
> >61000-4-2, IEC/EN 61000-4-3, IEC/EN 61000-4-4, IEC/EN 61000-4-5,
> >and IEC/EN 61000-4-6. The radiated E-field immunity is at least
> >3 V/m from 27 MHz to 1000 MHz, and greater than 6 V/m in the FM
> >broadcast band.
> >The E-field ten meters away from an antenna driven by a 2 kW PEP
> >transmitter is about 31 V/m, peak. Our phones were never
> >intended to work correctly when exposed to such high field
> >strengths. They should not be damaged by such fields, but it is
> >not astonishing that some users find malfunctions.
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